Rotationally adjustable fiber optic connector

ABSTRACT

A fiber optic connector assembly includes an outer connector housing defining an optic axis in a through passage. A first key is disposed in the passage at a given position angularly about the axis. An inner optical fiber plug terminates an optical fiber and is disposed in the passage and includes a second key movably positionable about the periphery of the plug to different selected positions of rotational adjustment for the plug. The second key is fixable at any selected position on the plug and is lockable with the first key on the housing to fix the angular position of the plug relative to the housing and, thereby, fix the rotational position of the optical fiber angularly of the optic axis.

FIELD OF THE INVENTION

This invention generally relates to the art of fiber optic connectorsand, particularly, to a connector wherein an optical fiber is angularlyadjustable about its axis and is maintainable in a selected rotationalposition of adjustment.

BACKGROUND OF THE INVENTION

Fiber optic connectors of a wide variety of designs have been employedto terminate optical fiber cables and to facilitate connection of thecables to other cables or other optical fiber transmission devices. Atypical fiber optic connector includes a ferrule that mounts and centersan optical fiber or fibers within the connector. The ferrule may befabricated of such material as ceramic. A ferrule holder or otherhousing component of the connector embraces the ferrule and may befabricated of such material as molded plastic. A spring typically isdisposed within the housing or ferrule holder such that the ferrule isyieldably biased forwardly for engaging another fiber-mounting ferruleof a mating connector device. In many fiber optic connectors, it isdesirable to angularly adjust the optical fiber within the connectorrelative to the fiber's longitudinal axis to achieve an optimum angularposition of the fiber whereat the insertion losses of the connector areat a minimum. In addition, the use of polarization maintaining (PM)fibers has been increasing, and it is essential that the PM fibers beproperly angularly oriented within the connector. Systems for angularlyadjusting such fibers have been complicated and not very cost effective.The present invention is directed to solving these problems by providingan extremely simple system that includes a fiber optic connectorassembly as well as a method for very simply and efficiently adjustingthe angular position of a fiber within a fiber optic connector.

SUMMARY OF THE INVENTION

An object, therefore, of the invention is to provide a new and improvedfiber optic connector assembly and method of rotationally adjusting anoptical fiber within the connector assembly.

In the exemplary embodiment of the invention, a fiber optic connectorassembly includes an outer connector housing defining an optic axis in athrough passage. A first key is formed in the passage at a givenposition angularly about the axis. An inner optical fiber plugterminates an optical fiber. The plug is disposed in the passage andincludes a second key movably positionable about the periphery of theplug to different selected positions of rotational adjustment for theplug. The second key is fixable at any selected position and is lockablewith the first key on the housing to fix the angular position of theplug relative to the housing and, thereby, fix the rotational positionof the optical fiber angularly of the optic axis. As disclosed herein,the second key is formed on a key ring that is rotatably mounted aboutthe plug. Therefore, the key ring can be rotated relative to the plug toposition the second key at different selected positions of rotationaladjustment for the plug.

According to an aspect of the invention, the first key is provided by arecessed keyway in the through passage of the housing. A key memberprojecting from the key ring forms the second key. In the preferredembodiment, a pair of the keyways is formed at opposite sides of thepassage, and a complementary pair of the key members is formed ondiametrical opposite sides of the key ring. The recessed keyways arelocated in a socket in the through passage of the housing for receivinga plug portion of the optical fiber plug. The key ring is disposed aboutand fixable to the plug portion. In another aspect of the invention, akey member projecting from the socket in the through passage of thehousing forms the first key and a recessed keyway in the key ringprovides the second key. The invention contemplates an extremely simplemeans for fixing the key ring to the plug at any selected position ofrotational adjustment. Specifically, the key ring is fixable to the plugby an adhesive injected between the key ring and the plug.

Finally, the invention contemplates a method of adjusting the rotationalposition of the optical fiber using the connector assembly describedabove.

Other objects, features and advantages of the invention will be apparentfrom the following detailed description taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of this invention that are believed to be novel are setforth with particularity in the appended claims. The invention, togetherwith its objects and the advantages thereof, may be best understood byreference to the following description taken in conjunction with theaccompanying drawings, in which like reference numerals identify likeelements in the figures and in which:

FIG. 1 is perspective view of a fiber optic connector assembly withwhich the invention is applicable;

FIG. 2 is an exploded perspective view of the connector assembly, withthe front housing part in section;

FIG. 3 is an enlarged perspective view of the front housing part andoptical fiber plug at the left-hand end of FIG. 2;

FIG. 4 is a view similar to that of FIG. 2, with the plug inserted intothe front housing part;

FIG. 5 is a view similar to that of FIG. 3, but with the plug insertedinto the front housing part;

FIG. 6 is a vertical section through the front housing part to show theinterengagement of the keys on the key ring with the keyways in thethrough passage of the front housing part;

FIG. 7 is a perspective view showing the key ring about to be assembledto the optical fiber plug;

FIG. 8 is a view similar to that of FIG. 7, but with the key ringassembled and fixed to the plug; and

FIG. 9 is a front elevational view of the connector assembly, with FIGS.9 a and 9 b being somewhat schematic illustrations to facilitate anunderstanding of a PM optical fiber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in greater detail, and first to FIGS. 1–3, theinvention is embodied in a fiber optic connector assembly, generallydesignated 10, which includes an outer connector housing, generallydesignated 12, having a front mating end 12 a, a rear end 12 b and athrough passage 14 extending between the ends and defining an optic axis16. Housing 12 is a two-part housing that includes a front housing part18 and a rear housing part 20. The front housing part has a pair oflatch openings 22 in opposite sides thereof for receiving a pair ofchamfered latch bosses 24 on opposite sides of rear housing part 20 whenthe housing parts are assembled as seen in FIG. 1. Typically, thehousing parts are molded of plastic material whereby latch bosses 24snap automatically into latch openings 22 when the housing parts areassembled. The front housing part also has a latch arm 26 that isflexible in the direction of double-headed arrows “A”. The latch arm hasa pair of latching ears 26 a on opposite sides thereof for latchingengagement with appropriate latch means on a complementary matingconnector, a mating adapter or other mating optical transmission device.Rear housing part 20 has a flexible actuator arm 28 having a serratedtop surface 28 a, for engagement by an operator, such as an operator'sthumb, for depressing latch arm 26 downwardly toward the connectorassembly. Pressing down on actuator arm 28 depresses flexible latch arm26 that is effective to unlatch latching ears 26 a from appropriatelatch means on the mating connector, thereby allowing unmating of theconnectors. Finally, a strain relief boot 30 projects rearwardly of therear housing part to provide strain relief for a fiber optic cable 32.

An inner optical fiber plug, generally designated 34 (FIGS. 2 and 3), isprovided for terminating at least one optical fiber of fiber optic cable32. The plug is disposed in through passage 14 in housing 12 as is seenbest in FIG. 5. The plug is disposed in the through passage for limitedaxial movement therein, as will be apparent hereinafter, the limitedaxial movement being on optic axis 16.

Optical fiber plug 34 includes a ferrule 36 that mounts and centers theoptical fiber of fiber optic cable 32, on optic axis 16. The ferrule maybe fabricated of such material as ceramic. A ferrule holder 38 embracesthe ferrule and may be fabricated of such material as molded plastic. Acoil spring 40 surrounds a rear tubular portion 44 of the optical fiberplug. The rear tubular portion may be integral with ferrule holder 38.The ferrule holder is larger in diameter than the rear tubular portion.A key ring 42 surrounds the rear tubular portion and abuts against arear surface 38 a of ferrule holder 38. A front end 40 a of coil spring40 engages a rear surface 42 a of key ring 42. A rear end 40 b of thecoil spring abuts against a shoulder (not visible in the drawings)within rear housing part 20.

Inner optical fiber plug 34 is inserted into front housing part 18 inthe direction of arrows “A” (FIGS. 2 and 3). Referring to FIGS. 4–6 inconjunction with FIGS. 2 and 3, a socket 46 (FIG. 6) is formed withinthrough passage 14 of front housing part 18 for receiving ferrule holder38 and key ring 42 of inner optical fiber plug 34. The ferrule holderabuts a front shoulder 46 a (FIG. 5) of socket 46 under the biasing ofcoil spring 40. The key ring includes a pair of radially outwardlyprojecting keys 48 on diametrically opposite sides of the key ring.Socket 46 includes a pair of axially extending keyways 50 formed thereinfor receiving keys 48 as seen most clearly in FIG. 6. Therefore, it canbe understood that, if key ring 42 is fixed to inner optical fiber plug34, the angular position of the plug within front housing part 18 and,thereby, connector assembly 10, also is fixed due to the positioning ofkeys 48 in keyways 50. FIG. 6 shows that the top key 48 and keyway 50are wider than the bottom key and keyway. This ensures that the opticalfiber plug and optical fiber are inserted into the front housing part inonly one orientation. It is to be noted that the key ring 42, in analternate embodiment (not shown), is formed such that it includes thekeyway. Accordingly, the socket 46 is formed with axially extendingkeys. Coupling and decoupling operations of the socket 46 and key ring42, as described above, therefore remains unchanged.

Before proceeding with further details of the invention, it should beunderstood that fiber optic connector assemblies, such as assembly 10,typically are “keyed” to the complementary mating connector, matingadapter or other mating optical transmission device. This “keying” isaccomplished by the vertical orientation of latch arm 26 and,especially, a front mounting portion 52 of the latch arm. As is clearlyseen in FIG. 6, mounting portion 52 and, likewise, latch arm 26 are“keyed” in a vertical direction. Correspondingly, keyways 50 in thefront housing part and keys 48 on key ring 52 similarly are “keyed” oraligned in this common vertical direction. Therefore, it can beunderstood that the angular orientation of inner optic fiber plug 34 andthe optical fiber that is terminated thereby, can be keyed or polarizedto the entire keyed orientation of the connector assembly. Stillfurther, it should be understood that connector assembly 10 is but oneexample of a connector assembly with which the invention is applicable.In the industry, connector assembly 10 is called an “LC” connector, butthe invention is equally applicable for “SC” connectors or otherconnector configurations.

Generally, the invention contemplates a system for rotationallyadjusting inner optical fiber plug 34 angularly about optic axis 16 tothereby rotationally adjust the angular position of the optical fiberwithin fiber optic cable 32, relative to keys 48 and keyways 50. Oncethe optical fiber plug (and optical fiber) are rotationally adjusted,the plug can be fixed in a selected position of adjustment andmaintained thereat in relation to the entire keying system of theconnector assembly, as described above.

Specifically, FIG. 7 shows key ring 42 removed from its assembledposition about rear tubular portion 44 of optical fiber plug 34. Inactual practice, if the plug is terminating a conventional optical fiberof fiber optic cable 32, plug 34 is “tuned” in order to achieve theoptimum angular orientation of the fiber relative to the keyed connectorassembly. As is known in the art, tuning is achieved by placing acomponent, such as plug 34, in a measuring apparatus that simulates theconnector assembly. The insertion losses of the plug (i.e., the opticallosses of the optical fiber) are measured in a given rotary position ofthe plug. An operator continues to rotate the plug until the measuringapparatus indicates the position of optimum orientation whereat theinsertion losses are at a minimum. Key ring 42 then is moved forwardlyin the direction of arrow “B” (FIG. 7) until the key ring is abuttedagainst ferrule holder 38 as shown in FIG. 8. This is done while holdingthe plug in its optimum angular orientation. Adhesive 60 (FIG. 8) thenis applied between the inside of the key ring and the outside of tubularmember 44 to maintain the key ring in its vertical orientation, asshown. The outside of tubular member 44 may be provided with a trough62, and the inside face of ferrule holder 38 may be provided with arecess 64, for receiving a sufficient amount of the adhesive material60. Now, with keys 48 of key ring 42 being fixed in the verticaldirection, and the fiber terminated within ferrule 36 being in itsoptimum angular orientation, the optical fiber plug and fixed key ringare inserted into socket 46 of front housing part 18 as shown above anddescribed in relation to FIGS. 4–6. It now can be understood that theoptimum angular orientation of the optical fiber within fiber opticcable 32 is keyed to the entire vertical keying system of the connectorassembly allowed by mounting portion 52 (FIG. 6) of the front housingpart, as described above. With plug 34 being freely rotatable within keyring 42 during timing of the plug, an infinite number of relativepositions of angular adjustment are afforded.

Although the invention has been described above in relation to aconventional optical fiber, the invention has considerable advantageswhen terminating a polarization maintaining (PM) fiber described belowin relation to FIGS. 9, 9 a and 9 b. First, a general background of PMfibers might be useful herein. In particular, a very useful property oflight that is utilized in fiber optics is the phenomena of polarization.Many fiber optic applications today are affected by the polarization ofthe light traveling through the fiber. Polarization dependent losses canadversely affect system performance. Therefore, analyzing, controllingand manipulating the polarization state of light in a fiber has becomeincreasingly important. There are different types of polarized light,but the simplest type is “linearly” polarized light in which theelectromagnetic field oscillates in a section plane. In mostapplications, it is desirable to preserve this form of polarization. Itmight be theoretically possible to produce perfectly linearly polarizedlight, but in actual practice, this is not the case. Thepolarization-extinction ratio (E) gives a measure of the portion of thebeam that is linearly polarized along a single axis. ER meters are usedfor this purpose.

With the above background of light polarization, it should be understoodthat when a normal optical fiber is bent or twisted, stresses areinduced in the fiber. These stresses, in turn, will change thepolarization state of light traveling through the fiber. If the fiber issubjected to any external perturbations, such as changes in the fiber'sposition or temperature, the final output polarization will vary. Thisis true for even short lengths of fiber and is undesirable in manyapplications that require a constant output polarization from the fiber.In order to solve these problems, polarization maintaining (PM) fibershave been developed whereby the light polarized along one axis of thefiber travels at a different rate than light polarized orthogonal tothat axis. This birefringent behavior creates two principal transmissionaxes within the fiber, known as the fast and slow axes. If the inputlight into a PM fiber is linearly polarized and oriented in a certaindirection, the output light from the fiber will also be linearlypolarized and oriented in the same direction. FIG. 9 b shows one type ofPM fiber that has the ability to maintain a linear polarization state.The fiber has a core 66 in which two propagation paths are created. Inother words, light coupled to the PM fiber is split into two orthogonalaxes. Ideally, the light travels independently along each axis. Linearlypolarized light launched into one axis will propagate solely along thataxis. The two axes may be created in the fiber either by changing theshape of the core or by applying asymmetric stress in the core. FIG. 9 bshows a fiber employing stress-induced method.

Specifically, a pair of stress rods 68 (FIG. 9 b) are embedded in thecladding 70 of the fiber. A plane 72 through the stress rods is referredto as the “slow axis”. A perpendicular plane 74 is called the “fastaxis”. The terms “slow” and “fast” refer to the relative propagationvelocity in each axis. By comparing FIG. 9 b with FIG. 9 a, it can beunderstood that if the PM fiber, generally designated 76, is terminatedwithin the optical fiber plug such that one of the axes (e.g., slow axis72) is aligned with keys 48 (FIG. 9 a), the PM fiber can be keyed to theentire vertical keying arrangement of connector assembly 10 describedabove. This is important because the angular orientation of PM fiber 76in connector assembly 10 must be rotationally aligned with a PM fiber ofa complementary mating connector or other fiber optic transmissiondevice. In other words, rotational alignment is required in connectingtwo PM fibers at a connector interface. The invention herein is veryuseful in achieving these goals, while the connector assembly still isapplicable for maintaining the angular orientation of a normal opticalfiber. The principal difference is rather simple. The angularorientation of optical fiber plug 34 for a normal fiber is “tuned” in ameasuring apparatus that measures optical losses, whereas the PM fiberis tested in an ER meter. Otherwise, the method of the invention is thesame for either fiber. Plug 34 is rotated to its optimum angularorientation; key ring 42 is fixed onto the plug while holding the plugat its optimum angular orientation, and then the key ring is used toprecisely align the inner optical fiber plug with the vertical keyedorientation of the connector assembly as described above.

It will be understood that the invention may be embodied in otherspecific forms without departing from the spirit or centralcharacteristics thereof. The present examples and embodiments,therefore, are to be considered in all respects as illustrative and notrestrictive, and the invention is not to be limited to the details givenherein.

1. A fiber optic connector assembly, comprising: an outer connectorhousing having a front mating end, a rear end and a through passageextending between the ends and defining an optic axis, the housinghaving a first key in the passage at a given position angularly aboutthe optic axis; an inner optical fiber plug for terminating at least oneoptical fiber of a fiber optic cable, the plug being disposed in thethrough passage in the housing with a front ferrule portion of the plugterminating the optical fiber at the front mating end of the housing,with the fiber optic cable extending from the rear end of the housing,the front ferrule portion including a ferrule holder; a key ringrotatably mounted about the ferrule holder and fixable on the ferruleholder at selected positions of rotational adjustment, the key ring andthe plug configured to enable the optical fiber and the plug to beinserted into the housing in only a single orientation, the key ringhaving a second key lockable with the first key on the housing once thekey ring is fixed to the ferrule holder on the plug; and wherein theplug can be rotated to the optimum position of angular adjustment of theoptical fiber relative to the optic axis, the key ring can be fixed tothe ferrule holder on the plug with the second key on the key ringaligned with the first key on the housing, and the keys can be locked tofix the angular position of the plug relative to the housing.
 2. Thefiber optic connector assembly of claim 1 wherein said first keycomprises a recessed keyway in the through passage of the housing, andsaid second key comprises a key member projecting from the key ring. 3.The fiber optic connector assembly of claim 2, including a pair of saidkeyways at opposite sides of the passage, and a complementary pair ofkey members on diametrical opposite sides of the key ring.
 4. The fiberoptic connector assembly of claim 2 wherein said recessed keyway islocated in a socket in the through passage of the housing for receivinga plug portion of the optical fiber plug, the key ring being disposedabout and fixable to the ferrule holder of the plug portion.
 5. Thefiber optic connector assembly of claim 1 wherein said key ring isfixable to the ferrule holder of the optical fiber plug at any of saidselected positions by an adhesive.
 6. The fiber optic connector assemblyof claim 1 wherein said second key comprises a recessed keyway in thekey ring and said first key comprises a key member projecting from thethrough passage of the housing.
 7. A fiber optic connector assembly,comprising: an outer connector housing defining an optic axis in athrough passage, with a first key in the passage at a given positionangularly about the axis; and an inner optical fiber plug disposed inthe passage and including a second key movably positionable about theperiphery of a ferrule holder on the plug to different selectedpositions of rotational adjustment for the plug, the plug terminating anoptical fiber, and the second key being fixable on the ferrule holder ofthe plug at any selected position and lockable with the first key on thehousing to fix the angular position of the plug in only a singleorientation relative to the housing and, thereby, fix the rotationalposition of the optical fiber angularly of the optic axis.
 8. The fiberoptic connector assembly of claim 7 wherein said first key comprises arecessed keyway in the through passage of the housing, and said secondkey comprises a key member for projection into the recessed keyway. 9.The fiber optic connector assembly of claim 8, including a pair of saidkeyways at opposite sides of the passage, and a complementary pair ofkey members on diametrical opposite sides of the key ring.
 10. The fiberoptic connector assembly of claim 8 wherein said recessed keyway islocated in a socket in the through passage of the housing for receivinga plug portion of the optical fiber plug, the key ring being disposedabout and fixable to the ferrule holder of the plug portion.
 11. Thefiber optic connector assembly of claim 7 wherein said second key isfixed to the ferrule holder of the optical fiber plug at any position ofrotational adjustment by an adhesive.
 12. The fiber optic connectorassembly of claim 7 wherein said first key comprise a recessed keyway inthe key ring and said second key comprises a key member projecting fromthe through passage of the housing.
 13. A method of adjusting therotational position of an optical fiber angularly of an optic axis in afiber optic connector assembly, comprising the steps of: providing anouter connector housing defining the optic axis in a through passage ofthe housing and with a first key in the passage at a given positionangularly about the axis; positioning an optical fiber plug in thepassage with a second key on the ferrule holder of the plug lockablewith the first key on the housing, and the second key being movablypositionable about the periphery of the ferrule holder of the plug todifferent selected positions of rotational adjustment for the plug, andwith the plug terminating an optical fiber; rotating the plug relativeto the second key to a selected singular position of rotationaladjustment corresponding to an optimum angular position of the opticalfiber; fixing the second key to the ferrule holder of the plug at saidselected position of angular adjustment; and locking the first andsecond keys in only a single orientation to hold the plug in theselected position of angular adjustment.
 14. The method of claim 13,including providing said second key on a key ring rotatably mountedabout the ferrule holder of the optical fiber plug.
 15. The method ofclaim 14, including providing said first key as a recessed keyway in thethrough passage in the housing, and providing said second key as a keymember projecting from the key ring.
 16. The method of claim 15,including providing a pair of said keyways at opposite sides of thepassage, and providing a complementary pair of key members ondiametrical opposite sides of the key ring.
 17. The method of claim 15,including locating said recessed keyway in a socket in the throughpassage of the housing for receiving a plug portion of the optical fiberplug, and disposing the key ring about the ferrule holder of the plugportion and fixing the key ring thereto.
 18. The method of claim 13,including the step of fixing the second key to the ferrule holder of theoptical fiber plug by an adhesive.
 19. The fiber optic connectorassembly of claim 13 wherein said second key comprises a recessed keywayin the key ring and said key comprises a key member projecting from thethrough passage of the housing.